The present invention relates to a metal thin layer type magnetic record medium suited for high density recording in magnetic disks, magnetic tapes, etc. used in the storage unit of electronic computers, video tape recorders, etc.
Ferromagnetic metal thin layer type magnetic record media obtained by forming a thin layer of a ferromagnetic metal (including cobalt, nickel, iron or an alloy comprising said metals as the main components) on a substrate formed of a polymer film (such as polyester film and polyimide film, aluminum alloy sheet, glass sheet etc.) by a vacuum film-forming method (such as vacuum deposition, sputtering, ion plating, etc.) exhibits a drastically improved recording density as compared with conventional coat-type magnetic record media. However, they are required to have a very thin magnetic layer and a smooth surface. Therefore, a different technique from that needed in coat-type media is necessary to satisfy these requirements with keeping the endurance reliability of the media.
In magnetic disk units used for external storage units of electronic computers, the so-called contact-start-stop (CSS) system is usually used. In the system, a magnetic head is contrived to float at a distance from the surface of a magnetic disc when the disk is in operation and contact with the surface of the disk during the time of stoppage. In order to endure the contact-sliding repetition of the magnetic head slider with the disc surface, the disc usually has an irregular-shaped surface formed by texture-finishing of the substrate surface, a carbon protective layer comprising graphite as the main component provided on the ferromagnetic metal thin layer and a lubricant layer formed on the surface of the carbon protective layer. As to the lubricant, the use of perfluoropolyethers unmodified or modified at the molecular terminal has been proposed (for example, U.S. Pat. No. 3,778,308 and JP-A-60-109028).
It has been proposed a metal thin layer type magnetic tape provided with a protective layer comprising diamond-like carbon on the ferromagnetic metal thin layer and coating thereon a specific fluoro-lubricant as the means for improving durability (JP-A-62-219314).
As to a magnetic disk, it is necessary to decrease the floating distance of the magnetic head for improving the recording density. In this case, improving the smoothness of the surface by decreasing the height of protrusions formed by texture-finishing leads to poor CSS durability. Additionally it gives rise to the so-called adsorption phenomenon. The adsorption phenomenon refers to a phenomenon wherein the lubricant on the disk surface gathers between the magnetic head and the disk at the time of stoppage of disk unit whereby the magnetic head is sticked to the disk surface.
The desired properties of the lubricant in the lubricant layer on the disk surface is such that the lubricant layer adheres strongly to both the protective layer surface beneath it and the magnetic head surface so as to form a coating layer on these surfaces, and simultaneously the molecules of lubricant are easily taken apart by a sliding action of the disk and the magnetic head. Since the surface of a perfluoropolyether molecule is almost wholly covered with fluorine atoms, the ether has a good property of being easily sheared between the molecules. However, it lacks a satisfactorily strong adhesive strength to the disk surface or to the magnetic head surface. Introduction of various polar groups into the molecular terminal of perfluoropolyether has been proposed to remedy the above-mentioned defect. However, due to the high molecular weight of several thousands of perfluoropolyether useful in practice, the effect of the introduction of polar groups is not appreciable and the effect of improving the disk durability is not marked. On the other hand, aliphatic hydrocarbons having polar groups typically represented by stearic acid and stearylamine have a high adhesive strength to various surfaces and molecular orientability. However, they exhibit a strong interaction between the molecules as compared with fluorinated hydrocarbons. Hence, when they are used as the lubricant, the intended durability can be hardly obtained. With regard to preventing the adsorption to the magnetic head, however, they show a greatly improved property attributable to the existance of polar groups as compared with perfluoropolyethers. The amino group has a merit of giving a particularly good adhesion strength to carbon-containing protective layers. However, on the other hand, it has a demerit of readily absorbing moisture at high humidities.
Further, it has been revealed that when a layer of a fluorolubricant is directly formed on the carbon-containing protective layer, the CSS durability and the head adsorption property at high temperatures or high humidities are reduced.
The present invention has been made to solve the above-mentioned problems. An object of the present invention is to improve the endurance reliability and the storage reliability of a metal thin layer type magnetic disk or magnetic tape having a carbon-containing protective layer.